Many actuators are adapted to move in one direction of a linear direction or a rotational direction. When an actuator is moved in two directions of the linear direction and the rotational direction, a motion direction converting mechanism for converting a motion direction mechanically is employed. However, when the motion direction converting mechanism converts the motion direction, noises are produced.
In a linear actuator in which a movable member (plunger) having a shaft is disposed inside a stationary member (yoke) so as to have a gap with the stationary member and a magnetic path is excited by a coil such that the movable member is moved in an axial direction of the shaft, Japanese Patent Laid-Open Publication No. 2002-78310 discloses an arrangement in which by making the gap nonuniform relative to axial displacement (stroke position) of the movable member, the movable member is moved in an axial direction of the shaft, i.e., in a linear direction and in a rotational direction having the axial direction as its rotational axis without using the motion direction converting mechanism.
Meanwhile, in a linear oscillator in which a first movable member (plunger) having a shaft is disposed inside a stationary member (yoke) provided in a casing so as to have a gap with the stationary member and a magnetic path is excited by a coil such that the first movable member is moved in an axial direction of the shaft, Japanese Patent Laid-Open Publication No. 2002-199689 discloses an arrangement in which a second movable member (amplitude control weight) serving to cancel inertia force of the first movable member is provided and spring members are provided among the casing, the first movable member and the second movable member such that not only by making the gap nonuniform relative to axial displacement (stroke position) of the first movable member, the first movable member performs on the basis of resonance in an axial direction of the shaft both reciprocating motion and motion in a rotational direction having the axial direction as its rotational axis without using the motion direction converting mechanism but vibrations of the first movable member due to axial inertia force can be reduced.
However, although the arrangements disclosed in Japanese Patent Laid-Open Publication Nos. 2002-78310 and 2002-199689 are advantageous in that the movable member can be moved in the two directions in response to axial displacement of the movable member by a simple construction without using the motion direction converting mechanism presenting a cause of noises, relation between motion of the movable member in the axial direction and motion of the movable member in the rotational direction is fixed by shape of the gap, so that the motion of the movable member in the axial direction and the motion of the movable member in the rotational direction cannot be controlled independently of each other and degree of freedom of operational control of the movable member is not so high.